Method and apparatus for curving sheets of glass and the like

ABSTRACT

The sheet to be curved, such as glass at a softening temperature, is advanced on a fixed curved bed formed by a series of curved rods having different angles of inclination to form an ascending convex bed with an increasing curvature profile. The sheet is thus gradually raised and simultaneously curved by sagging of the edges. The curved rods have aligned end sections mounted in the same horizontal plane and the inclinations progressively increase. The bed is followed by a bed of constant curvature profile formed by curved rods having the same inclination. Means are provided for independently adjusting the inclination of each rod. Particular ranges of spacing and rate of advance are given.

The present invention relates to the bending or curving of sheets ofmaterial in the plastic state such as sheets of glass brought tosoftening temperature.

It is known from U.S. Pat. No. 3,545,951 to use as a bending or curvingform a series of curved rods capable of pivoting about respective axespassing through their two ends and situated in the same horizontalplane. Each of these rods is rigidly connected to a crank arm and thevarious arms are connected to a common control bar. The rods thus form abed which is increasingly curved as the rods are raised higher by meansof the control bar. In addition, each rod is enclosed in a sleeve whichis flexible to allow bending but possesses torsional strength and whichis rotationally driven, thus causing the sheets of glass to be advanced.As the tangential velocity of these sleeves is identical at all points,no disturbing sliding or sticking problems occur during displacement ofthe sheets.

The curving or bending operation is carried out in the following manner.The curved rods are initially oriented in the horizontal plane of theirpivoting axes, and receive the sheet which is advanced in this plane bya conveyor. Then the control bar is displaced in a translationalmovement and, by means of cranks, simultaneously pivots the curved rodsso as to bring them into an inclined position with respect to the planeof advancement which corresponds to the desired curvature to be impartedto the sheet of glass, this position being maintained by the action of ajack.

When the bed is no longer flat, the sheet of glass at a softeningtemperature sags under its own weight or under the pressure of aregulatable counterform, and adopts the new shape provided by the rods.It is thus possible to obtain sheets having a desired degree ofcurvature, the maximum curvature being obtained when all the rods areturned to a right angle with respect to their original horizontalorientation. The sheet of glass is then advanced to a cooling unit whereit sets, cooling possibly being carried out rapidly so that the glass issimultaneously subjected to a thermal tempering step.

As soon as the sheet of glass has left the curving zone of theinstallation, the curved rods are returned to the plane of advancementof the conveyor so that the operating cycle can be repeated on a freshsheet of glass.

When a counterform is used, it is movable in translation and itsdisplacement is synchronized with the rotation of the sleeves. As aresult, it is still possible for the curving operation to be effectedwithout interrupting the advancement of the sheets. The use of acounterform makes it possible to operate at a lower temperature and thusobtain a higher quality product without reducing the rate ofmanufacture. However, the apparatus is fairly complicated and requiresaccurate regulation .

Whatever the mode of operation employed, one of the important advantagesis that a single apparatus can be used to provide sheets of glass withdifferent degrees of curvature simply by varying the degree ofinclination of the curved rods with respect to the horizontal plane ofadvancement.

A principal object of the present invention is to simplify the abovedescribed curving process and apparatus, while retaining the advantagesthereof.

In accordance with the invention, in the curving zone the sheets to becurved advance on a series of curved rods adjusted at fixed angles ofinclination, the said angles increasing from one rod to the next fromzero inclination (which corresponds to the position of the rod in thehorizontal plane of advancement) to a given maximum inclinationcorresponding to the final degree of curvature to be imparted to thesheets. The curved rods form an ascending convex bed with an increasingcurvature profile. Thus a sheet, during its continued advancement on thecurved rods is gradually raised and simultaneously curved. By virtue ofthis mode of operation, it is not necessary to provide mechanicalcontrol means for constantly pivoting the curved rods away from theplane of advancement and for returning them to this plane. On thecontrary, for a given line of curvature to be imparted to the sheet suchas glass, the inclination of each curved rod in a group of successiverods is selected once and for all and is normally not modified duringthe entire period that the device is used to produce a particularproduct line.

Preferably the curved rods are inclined in the opposite direction to thedirection of advancement of the sheets.

The difference in the angle of inclination from one rod to the next isadvantageously regulated in such a way that the level difference betweenthe peaks or the highest points of two successive curved rods rangesfrom 0-10 mm and preferably from 4-7 mm.

According to an advantageous mode of implementing the process, thesheets of glass are advanced into the curving zone at a rate of 6-18meters per minute on a group of 5-15 curved rods which are inclined withrespect to the horizontal at an angle which increases from one rod tothe next and with spacing of 6-16 cm between two successive rods. Therate of advancement of the glass depends on the thickness of the sheetsto be curved. The rate of advancement, may be high in the case of thinsheets and lower as the thickness increases. To provide some idea of thevalues involved, the rate of advancement advantageously varies from 6-18meters per minute when the thickness of the glass varies from 8-3 mm.For example, in the case of sheets having a thickness of 4 mm, goodresults are obtained with advancement rates of 12-14 meters per minute.

After passing through the curving zone per se, the sheets of glass areadvanced on a group of curved rods which are all inclined at the sameangle which corresponds to the line of curvature of the last rod in thecurving zone per se, i.e., corresponding to the final degree ofcurvature to be imparted to the sheets of glass. It is thus possible toaccomplish, if need, the curvature and to obtain stabilization of theshape imparted to the sheets of glass.

In the apparatus, the curved rods have aligned end sections forming axesof rotation, and the axes are mounted in the same horizontal plane.Means are provided for independently adjusting the inclination of eachrod.

Other objects, features and advantages of the method and the apparatusfor implementing the same will be made apparent in the followingdetailed description of a preferred embodiment thereof, with referenceto the accompanying drawings in which

FIG. 1 is a diagrammatic, longitudinal sectional view through a curvingapparatus, taken along the line I--I of FIG. 2;

FIG. 2 is a plan view of the conveyor device in the curving zone;

FIG. 3 is an elevational view of the means for regulating the angles ofinclination of the curved rods; and

FIG. 4 is a partial, plan view of FIG. 3 representing the ends of thepivoting shafts of the curved rods.

Referring to FIG. 1, a heating oven 1 is shown in which the sheets ofglass 4 are heated to the softening temperature. A curving zone 2 isdisposed downstream of the oven in which the sheets of glass areprovided with the desired degree of curvature. The curved sheets arecooled in zone 3, this cooling operation possibly being carried outrapidly by means of air jets to simultaneously subject the sheets ofglass to a thermal tempering step. The sheets are advanced through theinstallation in a horizontal position.

The initially flat sheets are advanced in the heating oven bycylindrical rollers 13 which are driven in rotation. Thereafter, theconveying rollers comprise curved rods 5 pivotably mounted at their twoaligned ends in the frame 6 (FIG. 2). These curved rods are enclosed inflexible tubular sleeves 7 possessing torsional strength. The sleevesare driven by means of a motor 9 through the intermediary of chains 10,11, 12 and toothed pinions 8 meshing with the chains and affixed to theends of the sleeves.

The axes of the curved rods are preferably spaced apart by approximately6-15 cm. The tubular sleeves 7 may have a diameter of 40-60 mm.

All the rods 5 have the same height, for example 120 mm. They areoriented in the upstream direction and inclined with respect to thehorizontal. Their angles of inclination in the curving zone are adjustedso that the angles increase from one rod to the next from the lefthandside to the righthand side of the figure. The first rod 5a, for example,is maintained in the plane of advancement, i.e. its point of contact issituated in the plane of the lower face of the flat sheet of glass 4issuing from the oven 1. The following rod 5b is adjusted at an angle ofinclination such that the position of its high point (in the axis of theoven) is located between 0 and 10 mm and preferably between 4 and 7 mmabove the corresponding point on the rod 5a. The rod 5c is adjusted at aslightly higher angle of inclination and thus projects, in its medianregion, above the level of the preceding rod by about 4-7 mm. The sameapplies to the succeeding rods 5b-5m which are each slightly moreinclined with respect to the horizontal than the preceding rod. In thiscurving zone the spacing of the curved rods is advantageously in therange of 6-16 cm.

After passing over the first curved rod 5a, the sheet of glass 4 issuingfrom the oven 1 in the direction of the arrow F passes over the secondrod 5b and is thus slightly raised, mainly in its median region, and toa lesser extent in its lateral regions. The leading edge of the sheet ofglass is thus moved downstream and is gradually raised to the heightcorresponding to the inclination of the curved rods situated at theother end of the curving zone, this height depending on the final lineof curvature to be imparted to the sheets of glass.

The number of curved rods whose angles of inclination are so adjustedcan amount to 5-15 and depends on the degree of curvature. For example,good results are obtained when, for a radius of curvature of 1000-1500mm. the curving zone per se, as shown in the drawings, comprises twelvecurved rods 5b-5m whose angle of inclination increases from one rod tothe next. In the case of a desired radius of curvature of 2000 mm. goodresults were obtained from the point of view of the optical qualities ofthe curved glass using only eight differently inclined curved rods.

The rate of advancement at which the sheets of glass are displaced onthe rods may be increased as the thickness of the sheets decreases. Togive some idea of the values involved, the rate of advancementadvantageously varies from 6-18 meters per minute when the thickness ofthe sheets decreases from 8-3 mm. In the case of sheets having athickness of 4 mm, good results are obtained, for example, withadvancement rates of 12-14 meters per minute.

The temperature of the sheets of glass in the curving zone may be on theorder of 620° C.

At the end of the curving zone A (rods 5a-5m) per se, i.e., the zone inwhich the curved rods possess an increasing angle of inclination fromone rod to the next, there is provided a series of curved rods 5n whichall possess the same angle of inclination corresponding to the angle ofinclination of the last rod 5m in the curving zone A. The number ofthese rods 5n whose inclination corresponds to the desired final line ofcurvature may range from 5-15.

Zone B, (rods 5n) in which the curved rods all possess the same angle ofinclination, is used to stablize the curve imparted to the sheets ofglass. In this region the sheets of glass conform more completely,during their advancement movement, to the line of curvature of the bedformed by the curved rods. In this region the curved rods possess mutualspacing of 6-16 cm. and the sheets of glass are displaced at a ratewhich preferably corresponds to the rate of advancement in the curvingzone per se.

FIGS. 3 and 4 show the elements used to adjust the angles of inclinationof the curved rods. For reasons of clarity, the difference in the angleof inclination from one rod to the next has been exaggerated. Eachcurved rod 5 is equipped at one end with a clamping means 15 which isfirmly tightened on the end of the rod by the screw 16. Each clampingmeans 15 includes an apertured lug 17 in whose orifice is coupled thebent end of the threaded bolt 18. Together with the threaded link 19 andthe bolt 20 connected to the frame, bolt 18 forms a turnbuckle by meansof which the distance between the two bolts 18 and 20 may be varied inthe known manner by simply rotating the link 19. The bolt 20 is pivotedto the beam 22 of the curving apparatus by means of lug 21.

To save space, in view of the proximity of the pivoting shafts of thesuccessive curved rods, the clamping means 15 are alternately staggeredalong these shafts, as shown in FIG. 4.

We claim
 1. A process for bending to a predetermined curvature a sheetof material in the plastic state, such as a sheet of glass brought tothe softening temperature, on a curved bed formed by a series of curvedrods mounted for pivoting about axes disposed in the same horizontalplane, which comprises inclining the curved rods at different angles ofinclination with respect to said horizontal plane to form an ascendingconvex bed with a curvature profile which increases progressively to acurvature corresponding to the predetermined curvature which is to beimparted to the sheet, maintaining the rods at said angles ofinclination to form a fixed bed having said increasing curvature profileand advancing the sheet on said fixed bed in the direction of increasingcurvature thereof by a rotationally driven sleeve disposed about atleast one of the curved rods.
 2. A process according to claim 1 in whichsaid curved rods have the same curvature with similar aligned endsections mounted in said horizontal plane and said angles of inclinationthereof progressively increase in the direction of advancement of thesheet.
 3. A process according to claim 2 in which the sheet is advancedbeyond said curved bed on a bed having a constant curvature profilecorresponding to the predetermined curvature to be imparted to saidsheet which is formed by a series of similarly curved rods having thesame angle of inclination.
 4. A process according to claim 1 in whichthe difference in height of the peaks of successive curved rods is inthe range of 4-7 millimeters.
 5. A process according to claim 1 in whichsaid bed has 5-15 curved rods spaced apart by 6-16 centimeters and thesheet of glass is advanced thereon at the rate of 6-18 meters perminute.
 6. A process according to claim 1 in which the product of thethickness of said sheet times its rate of advancement is of the order of0.05 square meters per minute.
 7. Apparatus for bending to apredetermined curvature a sheet of material in the plastic state, suchas a sheet of glass brought to softening temperature, which comprises aseries of curved rods forming a curved bed for receiving said sheet,said rods having aligned end sections forming respective axes ofrotation, means for pivotally mounting said curved rods with the axes ofrotation thereof in the same horizontal plane, a rotationally drivensleeve disposed about at least one of said rods for advancing a sheetalong said bed, and means for holding said rods at different angles ofinclination to form a fixed ascending convex bed having a curvatureprofile which increases progressively in the direction of advancement ofthe sheet to a curvature corresponding to said predetermined curvature.8. Apparatus according to claim 7 in which said curved rods have thesame curvature and said angles of inclination progressively increase insaid direction of advancement.
 9. Apparatus according to claim 7including a further series of curved rods positioned downstream of saidseries of rods and having aligned end sections forming respective axesof rotation, the axes of rotation of said further series being in thesame horizontal plane as the axes of the first-mentioned series, saidfurther series of rods being held at the same angle of inclination toprovide a bed having a constant curvature profile corresponding to saidpredetermined curvature.
 10. Apparatus according to claim 7 includingindependent means for adjusting the angle of inclination of each curvedrod.